The objective of this study is to compare the analgesic effectiveness of lumbar intrathecal enkephalin (DADLE), a delta opiate-receptor agonist, to that of intrathecal morphine, a mu-receptor agonist, in cancer patients with varying degrees of tolerance to conventional (mu-receptor) narcotics. Under double-blind conditions, patients with pain below the waist will receive DADLE and morphine in random order two days apart, by lumbar puncture. Intrathecal drug doses will be determined by patients' prior systemic opiate dose. Those on the equivalent of morphine 10 mg IM q4h or less will receive intrathecal DADLE .25 mg or morphine 1 mg. Those on higher systemic opiate doses will have doses of both intrathecal drugs raised proportionately. Reported pain levels, vital signs, alertness, mood, neurological function and side effects will be followed for 48 hours. Pain relief and side effects of the two drugs will be compared for the entire group and for the halves of the group previously on higher and lower systemic narcotic doses.